This invention relates to a base construction comprising a hot plate for a coffee-making apparatus of the type designed to have water brought to a boil in a closed container, whereupon the water is pressed through a riser pipe into a funnel, where boiling water extracts aromas and flavour from the ground coffee, whereupon the finished coffee beverage is filtered back into the closed container through a filter placed at the outlet of the funnel.
The patent No. EP 98122329.0 exemplifies the principle of heating the water to boiling point by means of more than one hot plate, where one hot plate is used for boiling at high power, and another hot plate is used to maintain the temperature which is most beneficial to the finished coffee beverage. Naturally, a different, lower level of power is used for this purpose.
A similar device for making tea is known from EP 292 649, where the apparatus comprises at least one base consisting of a hot plate. As this known method is aimed specifically at tea-making, it is only marginally relevant here.
From the known designs, it is known that boiling ceases when a sudden and strong rise in temperature occurs, which indicates that the water has evaporated. This leaves the hot plate with a surface of dried-out sediments, which carbonate over time and become unpalatable. Moreover, the hot plate will still be considerably warmer than the coffee beverage upon the return of said beverage; this will damage the aroma of the beverage when it hits the hot plate. Another feature of the known design is that the base is sealed by means of either soldering or fastening by means of screws while using a seal between the hot plate and the base construction; this entails great cost in terms of assembly and production.
Consequently, the object of the present invention is to provide a sealed base which comprises a hot plate for a coffee-making apparatus where the hot plate does not suddenly boil dry, while the finished coffee beverage is treated with care. Moreover, reliable sealing of the hot plate must be provided, using simple means and without the use of tools.
According to the principles of the present invention, this objective is met by means of a base construction which comprises a hot plate for a coffee-making apparatus of the type initially mentioned, where the hot plate and the inside bottom of the closed container are placed in a position where the normal of the hot plate is at no point vertical during boiling, where the hot plate has been sealed towards a radial protrusion, which forms a flange in the bottom, by means of a U-shaped seal, where the points of the U are positioned on separate sides of the hot plate, and where the U-shaped seal is fastened in the flange by means of a clamping ring which squeezes the seal to the protrusion.
With a base according to the principles of the present invention, the evaporating water will drain the hot plate gradually, thus ensuring a continuous remaining volume of water in the lower part of the base. Thus, any sediments present in the water can be kept continually suspended, so that they do not contaminate the hot plate when it dries out and is subsequently reheated. As a result, the hot plate is heated inhomogenously, thus facilitating a more appropriate distribution of temperature across the hot plate, as the thermo-sensor is able to respond with greater speed when it is not in contact with the boiling water. The remaining water ensures that the finished coffee beverage is not subjected to a shock when meeting the hot plate, which still has a high temperature, when the finished coffee beverage returns to the closed container, thus running into the remaining volume present.
In one appropriate embodiment of the base according to the principles of the present invention, a locking ring is inserted between the clamping ring and the cylindrically upright part of the flange with a view to ensuring that the clamping ring is not loosened. Thus, the base appears as a self-locking system, which cannot be loosened unintentionally. The advantage is that water cannot seep into the electronics positioned beneath the base construction.
An appropriate construction can be achieved by having the outer surface of the U-yoke faintly arrow-shaped, with the greatest thickness outside the edge of the hot plate. This ensures easy mounting of the base with the U-shaped seal and moreover ensures that there is space for radial dilation of the seal, so that a very tight construction is achieved.
In a appropriate embodiment of the base construction according to the principles of the present invention, it is proposed that the thermo-sensor monitoring whether the hot plate boils dry should be placed in the area of the hot plate which is first to be exposed in the event of the water boiling away. Thus, the temperature is increased gradually, and any sediments present in the remaining volume can remain suspended and avoid drying out and burning.
A further appropriate embodiment of the base construction according to the principles of the present invention is designed so that the hot plate features two electrical circuits, a high-power circuit and a low-power circuit, where each circuit features a regulator circuit (not shown) in connection with a standard contactor where the regulator circuits are connected to the external power circuit. In this connection, both the high-power and low-power circuits are standard types with bimetal contacts controlled by thermo-sensors. It will be particularly appropriate for the hot plate to be fitted in a known manner with a contactor, which with respect to the low-power circuit is fitted with an additional contact pin which is fastened to the contactor by means of a guide tongue and a number of tongue pieces and locking hooks, and which is also fitted with a supply contact and a pair of spring pins ensuring contact to the low-power circuit. In this manner, any spring movement will occur perpendicular to the contact surface, and thus this construction ensures that friction cannot occur against the contact point of the circuit, which thus cannot be worn.
Further appropriate embodiments according to the principles of the present invention appear from the dependent claims.